It belongs to a species referred to as Vulpin Serpent by Rhomboid Vreedle, though whether this is the creature's official name or just a common name or nickname Rhomboid used is unknown.
For the most part, the Two-Headed Snake resembles an Earth snake species of green and brown coloration, with certain details to make it look more alien, such as the longer than average fangs, the frills or horns at the back of the head, the four eyes and of course, the two heads. The creature's full design is never seen, but it's implied based on the structure of the cave it was in that each head was at the opposite ends of the snake's body.
Additionally, the creature is enormous, far bigger than even the largest extinct snakes and so massive that its heads alone dwarf nearly if not all of Ben's playable aliens (with the possible exception of Humungousaur).
Ben 10 Alien Force: Vilgax Attacks
Shortly after arriving to Vulpin in search of Max, Ben defeated a few Vulpimancers and some of Vilgax's drones and awakened a large bicephalous reptile aiming to kill Ben for no other reason than him being in its territory.
Thanks to Swampfire, Ben was able to defeat the snake by countering its powers with Swampfire's own and inspected the cave the snake was in before being destroyed, finding a health upgrade. Upon leaving the snake's resting place, Ben continued his journey looking for Max.
Ben 10: Galactic Racing
Several bigger members of this species appear in Ben 10: Galactic Racing, on the Vulpin stages known as the "Trashy Twist" and "The Sludgeway", getting into the factory the stages are set in. The Vreedle Brothers assure the racers that the serpents are more interested in the sludge than in eating them.
Powers and Abilities
Putting its superior size to good use, the Two-Headed Snake mainly attacked with its heads, swiping and smashing them around like clubs or biting down on whatever was in its reach. Its tough scales made it impervious to all manner of attack from Ben's alien transformations, and thanks to the fact that there was a river of sludge between the snake's cave and where Ben was, Ben's only option at first was to get closer and attack the snake, which put him in a vulnerable position.
Additionally, the snake could spew out a green noxious flammable gas out of each of his mouths.
Due to the aforementioned toxic gas being flammable, once Ben used Swampfire's fireballs and ignited the gas down the snake's neck, the creature could be harmed and was quickly killed.
- The Two-Headed Snake's design is reminiscent of the Amphisbaena and the Bȧa-ta, two monstrous serpents from Greek and Egyptian myths respectively that had heads on each end of their bodies.